The regional distribution of ventilation and blood flow will be measured in man by the radioactive xenon method. The distribution of inhaled boluses of 133Xenon in air and in a helium/oxygen mixture will be measured at varying inspiratory flow rates to examine the influence of inspired gas density and of flow rate on regional ventilation in normal subjects and in patients with asthma and with chronic obstructive lung disease. The results of these experiments may permit some conclusions about whether regional differences in the contribution of "small airways" to the resistance to inspiratory flow significantly influence inspired gas distribution in obstructive lung disease. In patients with progressive systemic sclerosis (scleroderma) the regional lung blood flow distribution will be measured during acute hypoxia and during induced Raynaud's phenomenon. The purpose of these experiments is to look for evidence of an acute increase in upper zone blood flow such as might occur if a phenomenon analogous to Raynaud's phenomenon occurs in the lungs. BIBLIOGRAPHIC REFERENCES: Dawson, A., Rocamora, J.M. and Morgan, J.R. Regional lung function in chronic pulmonary congestion with and without mitral stenosis. Amer. Rev. Resp. Dis. 113, 51-59, 1976.